1. Field of the Invention
This invention relates to a semiconductor device, such as an LED print head for an electro-photographic printer, and a method of manufacturing the same.
2. Description of the Related Art
FIG. 26 is a perspective view of part of an LED print head 900 according to a related art and FIG. 27 is a top plan view of part of an LED array chip 902 for the LED print head in FIG. 26. In FIG. 26, the LED print head 900 comprises a substrate 901, the LED array chip 902 formed on the substrate 901, and a driving IC chip 904 formed on the substrate 901. Electrode pads 903 of the LED array chip 902 and electrode pads 905 of the driving IC chip 904 are connected by bonding wires 906, and the electrode pads 909 of the driving IC chip 904 and electrode pads 910 of the substrate 901 are connected by bonding wires 911.
In Japanese Patent Application Kokai Number 10-063807 (hereinafter xe2x80x9cpatent documentxe2x80x9d), a light emitting device having thin film structure is disclosed. In the patent document, it is described that a plurality of thin films forming the light emitting device are developed and then elements are separated by etchant.
However, in the LED print head 900, as shown in FIG. 27, large electrode pads 903 and 905 (for example, 100 xcexcmxc3x97100 xcexcm) are provided on the LED array chip 902 and the driving IC chip 904, respectively, for electrically connecting the LED array chip 902 and the driving IC chip 904 by the bonding wires 906. Accordingly, it was difficult to make the size of the LED array chip 902 small, which made it difficult to reduce the material cost. In the LED array chip 902, a light emitting section 907 is located in a region of approximately 5 xcexcm deep from the surface. However, in the LED print head in FIG. 26, it has been required that the thickness of the LED array chip 902 is made substantially equal to that of the driving IC chip 904 (for example, 250 xcexcm to 300 xcexcm) to secure a stable wire bonding yield. Accordingly, it was difficult to reduce the material cost of the LED array chip 902 for the LED print head 900.
In the patent reference, it is disclosed that the light emitting device having the thin film structure is provided with an electrode pad for a soldering ball for connecting the electrode pad to a discrete pad. Accordingly, it was difficult to reduce the size of the light emitting device.
Also, as described above, in the patent reference, it is disclosed that the elements are separated by etchant. However, a critical technical problem is not disclosed in the patent reference that some materials for the respective semiconductor thin films and/or some etchants may cause etching of not only parts required for the separation or removal of the semiconductor thin films but also other parts, such as inter-layer insulating thin films and wiring materials.
Accordingly, it is an object of this invention to provide a semiconductor device, wherein the miniaturization of the device and cost reduction of the material can be achieved, and a method of manufacturing a semiconductor device, wherein yield reduction caused by the etching problem is prevented besides the achievement of the miniaturization of the device and cost reduction of the materials.
According to the invention, a method of manufacturing a semiconductor device comprises the steps of forming a separation layer on a second substrate, forming the semiconductor thin film including all or part of semiconductor elements on the separation layer, forming a protection layer on the semiconductor thin film such that the protection layer covers part of the semiconductor thin film, forming a plurality of etching grooves by etching a region of the semiconductor thin film, which is not covered by the protection layer, so that the etching grooves divide the semiconductor thin film into a plurality of semiconductor thin sub-films, the etching groove reaching the separation layer, etching the separation layer to make a plurality of discrete semiconductor thin films from the semiconductor thin sub-films, adhering the discrete semiconductor thin films onto the surface of the first substrate, and removing the protection layer. The protection layer is made of a material which has etching resistance against etchants used in the steps of forming the etching grooves and etching the separation layer. Here, the etching resistance property means that the function of the protection layer of protecting the semiconductor thin film is not damaged by the followings reasons:
1. The material of the protection layer is not dissolved, decomposed, or broken by the etchant for the steps of forming the etching grooves and etching the separation layer.
2. The adhesion of the interface between the protection layer and the surface of the semiconductor thin film is not damaged by the penetration of the etchant through the interface.
3. The adhesion of the interface between the protection layer and the surface of the semiconductor thin film is not damaged by the penetration of the etchant through the protection layer up to the interface.